Cliftonville defender Michael Newberry has died suddenly at the age of 27.
The English defender joined the club in the summer and made 24 appearances for the Reds.
Newberry, who started his career with hometown club Newcastle United also had a spell with Linfield, where he won two Irish Premiership titles.
Cliftonville's game against Dungannon Swifts and Linfield's match with Larne on Monday night have both been postponed.
In a statement posted on the club's website, Cliftonville said they were "devastated".
"Our condolences are extended to Michael's family and friends, as well as the many team-mates he played with during his career, and fans who will be shaken and saddened by this heartbreaking news," their statement added.
"Rest in peace, Newbs."
Linfield said "the thoughts and prayers of everyone at the club are with Michael's family and friends at this very sad time."
The NI Football League said they "pass on our heartfelt condolences to Michael's family, friends and everyone connected with Cliftonville Football Club at this sad time."